Field of the Invention
The present invention relates to a variable valve that is adjusted to be opened and closed by flow pressure of exhaust gas, and more particularly, to a variable valve in which two gates open and close an opening, and springs connected with the gates are set to have different spring properties to allow the variable valve to be partially opened.
Description of Related Art
An exhaust system, which discharges exhaust gas produced in an engine to a rear side of a vehicle body, includes a muffler that reduces exhaust noise when exhaust gas is discharged.
The muffler mounted in a vehicle is formed in a cylindrical shape having a predetermined shape, and a plurality of pipes and baffles are mounted in the muffler so as to reduce exhaust noise by inducing expansion of exhaust gas, resonance, and absorbing noise when exhaust gas flows.
Meanwhile, because the amount of exhaust gas produced in the engine varies with traveling situations of the vehicle, a variable valve is mounted in the muffler in order to more efficiently adjust exhaust efficiency and performance in inhibiting noise in accordance with the traveling situations.
The variable valve serves to reduce exhaust noise by closing a gate when the engine is rotated at a low speed, and to improve exhaust performance by opening the gate when the engine is rotated at a high speed.
Typically, the variable valve is mounted to any one of the pipe mounted in the muffler and the baffle that forms a wall surface so as to divide an internal space of the muffler, and has a structure as illustrated in FIG. 1. That is, the variable valve in the related art is configured so that a gate 2 is rotatably coupled to a housing 1 so as to open and close an opening in the housing 1.
The gate 2 is mounted to be rotatable about a shaft 3a which is mounted on hinge support portions 1a formed at one side of the housing 1 and serves as a rotation axis, and a coil-shaped torsion spring 3, which has one end in contact with the gate 2 and elastically presses the gate, is coupled to the shaft 3a. 
The variable valve in the related art, which is configured as described above, is operated so that the gate 2 is opened when pressure of exhaust gas exceeds elastic force of the torsion spring 3, and the gate 2 is maintained in a closed state when pressure of exhaust gas is lower than elastic force of the torsion spring 3.
That is, the variable valve is closed in a low speed section to attenuate low-frequency noise, and gradually opened in middle and high speed sections to attenuate high-frequency noise and has no effect on output of the engine by reducing resistance of exhaust gas.
However, when the variable valve in the related art is used under an environment having a predetermined high temperature, spring properties of the torsion spring 3 significantly deteriorate and thus it is impossible to precisely control a flow rate, and as a result, there is a problem in that when the gate 2 is opened up to a designed value or larger, interference with peripheral components occurs.
In the case of the variable valve in the related art, one end of the torsion spring 3 is just in point contact with the gate 2 to support the gate 2, and as a result, there are problems in that abnormal noise occurs due to rattling of the gate 2 because the torsion spring 3 does not durably support the motion of the gate 2, and abnormal touching noise occurs due to a collision between the gate 2 and the housing 1 when the gate 2 is closed.
In the case of the variable valve having a structure in the related art, an opening degree of the gate 2 is determined by a spring constant of the torsion spring 3, but there is a situation in which under an actual vehicle condition, problems of exhaust booming need to be solved by dividing the time when the exhaust booming occurs into when the vehicle is idling and when the vehicle travels.
That is, in a situation in which flow conditions of exhaust gas vary, it is difficult to cope with noise, vibration and harshness (NVH) performance of the vehicle and efficiently control an opening degree of the gate 2 by using only the single torsion spring 3 like the structure in the related art.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.